U.S. patent number 4,320,044 [Application Number 06/197,389] was granted by the patent office on 1982-03-16 for self-extinguishing silicone rubber containing aluminum hydrate.
This patent grant is currently assigned to Toray Silicone Company, Ltd.. Invention is credited to Akito Nakamura.
United States Patent |
4,320,044 |
Nakamura |
March 16, 1982 |
Self-extinguishing silicone rubber containing aluminum hydrate
Abstract
A mixture of polydiorganosiloxane, aluminum hydrate, and
gamma-type iron sesquioxide or ferroferric oxide can be cured to
provide a silicone rubber with improved self-extinguishing
properties and heat stability.
Inventors: |
Nakamura; Akito (Ichihara,
JP) |
Assignee: |
Toray Silicone Company, Ltd.
(Tokyo, JP)
|
Family
ID: |
15873386 |
Appl.
No.: |
06/197,389 |
Filed: |
October 16, 1980 |
Foreign Application Priority Data
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Dec 25, 1979 [JP] |
|
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54/168732 |
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Current U.S.
Class: |
524/413; 524/91;
524/115; 524/398; 524/588; 524/783; 524/863; 524/437; 524/190;
524/431; 524/781; 524/860 |
Current CPC
Class: |
C08K
3/22 (20130101); C08K 3/016 (20180101); C08K
5/14 (20130101); C08K 5/0066 (20130101); C08K
5/14 (20130101); C08K 5/0066 (20130101); C08L
83/04 (20130101); C08K 3/016 (20180101); C08K
5/14 (20130101); C08L 83/04 (20130101); C08K
3/22 (20130101); C08K 3/016 (20180101); C08L
83/04 (20130101); C08K 3/22 (20130101); C08L
83/04 (20130101) |
Current International
Class: |
C08K
3/00 (20060101); C08K 3/22 (20060101); C08K
003/22 () |
Field of
Search: |
;260/37SB,45.75P |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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50-97644 |
|
Aug 1975 |
|
JP |
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51-35501 |
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Oct 1976 |
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JP |
|
Primary Examiner: Hoke; V. P.
Attorney, Agent or Firm: Burrousch; Roger H.
Claims
That which is claimed is:
1. A mixture comprising
(A) 100 parts by weight of a polydiorganosiloxane represented by an
average unit formula
wherein each R is selected from a monovalent hydrocarbon radical
and a halogen-substituted monovalent hydrocarbon radical, and a has
an average value of from 1.98 to 2.05,
(B) 50 to 300 parts by weight of aluminum hydrate with an average
particle size of .ltoreq.50 .mu.m, and
(C) 0.1 to 30 parts by weight of an oxide selected from the group
consisting of gamma-type iron sesquioxide, ferroferric oxide, and
mixtures thereof, said oxide being in the form of an extremely fine
powder, and said ferroferric oxide having a formula (FeO).sub.x
(Fe.sub.2 O.sub.3).sub.y in which the ratio of x/y is from 0.05/1
to 1.0/1.
2. The mixture according to claim 1 further comprising an organic
peroxide.
3. The mixture according to claim 1 further comprising at least one
filler selected from the group consisting of a reinforcing filler
and a bulking filler.
4. The mixture according to claim 3 further comprising an organic
peroxide.
5. The mixture according to claim 1 further comprising a
self-extinguishing enhancing material selected from the group
consisting of finely powdered copper, calcium carbonate, calcium
zirconate, zirconium silicate, manganese carbonate, titanium
dioxide, cobalt organic acid salts, organophosphorus compounds, azo
compounds, triazole compounds, and sulfur-free carbon black.
6. The mixture according to claim 5 further comprising an organic
peroxide.
7. The mixture according to claim 6 further comprising at least one
filler selected from the group consisting of a reinforcing filler
and a bulking filler.
8. The mixture according to claim 2 in which the
polydiorganosiloxane of (A) has a degree of polymerization of
.ltoreq.1000, the aluminum hydrate of (B) is present in an amount
of 100 to 200 parts by weight, the oxide of (C) is present in an
amount of from 1 to 20 parts by weight and the organic peroxide is
present in an amount of from 0.3 to 6 parts by weight per 100 parts
by weight of (A).
9. The mixture according to claim 1 in which the oxide of (C) is
the gamma-type ferric oxide.
10. The mixture according to claim 8 in which the oxide of (C) is
the gamma-type ferric oxide.
11. The mixture according to claim 1 in which the oxide of (C) is
the ferroferric oxide.
12. The mixture according to claim 8 in which the oxide of (C) is
the ferroferric oxide.
13. The mixture according to claim 8 further comprising at least
one filler selected from the group consisting of a reinforcing
filler and a bulking filler.
14. The mixture according to claim 13 in which there is present a
reinforcing silica filler.
15. The mixture according to claim 14 further comprising an
organosilicon compound selected from the group consisting of
diphenylsilanediol, an alkoxysilane and low molecular weight
hydroxyl endblocked polydimethylsiloxane.
16. A self-extinguishing silicone rubber obtained by heat
vulcanizing the mixture of claim 2.
17. A self-extinguishing silicone rubber obtained by heat
vulcanizing the mixture of claim 4.
18. A self-extinguishing silicone rubber obtained by heat
vulcanizing the mixture of claim 6.
19. A self-extinguishing silicone rubber obtained by heat
vulcanizing the mixture of claim 8.
20. A self-extinguishing silicone rubber obtained by heat
vulcanizing the mixture of claim 13.
21. A self-extinguishing silicone rubber obtained by heat
vulcanizing the mixture of claim 15.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates a silicone rubber having an improved
self-extinguishing property.
2. Description of the Prior Art
Although silicone elastomers exhibit various excellent properties,
they are inflammable and attempts have been made to make them
self-extinguishable by various methods. For example, a
platinum-containing material has been added to silicone rubber
compounds as shown by U.S. Pat. No. 3,514,424, issued May 26, 1970,
to Noble et al., a platinum compound and (FeO).sub.x (Fe.sub.2
O.sub.3).sub.y where the ratio of x/y is from 0.05/1 to 1.0/1 have
been added to silicone rubber compounds as shown by Japanese Pat.
No. Sho 51(1976)-35501, published Oct. 2, 1976, to Hatanaka et al.
and a platinum compound and .gamma.-type iron sesquioxide have been
added to silicone rubber compounds as shown by Japanese Pat. No.
Sho 53(1978)-44501. It is known from U.S. Pat. No. 3,965,065,
issued June 22, 1976, to Elliott, to make silicone rubber
containing aluminum hydrate and a combination of aluminum hydrate
and chloroplatinic acid hexahydrate.
As pointed out in the above paragraph, platinum or a platinum
compound is an indispensable additive for self-extinguishing
silicone rubber compositions and imparts a relatively strong
self-extinguishing capacity to silicone rubbers. However, platinum
or platinum compounds are very expensive so that the cost of
production of the silicone rubber is high. The presence of platinum
or a platinum compound adversely affects the heat-stability
property of silicone rubber. These are the drawbacks of the
self-extinguishing silicone rubbers produced by the methods using
platinum or platinum compounds.
SUMMARY OF THE INVENTION
Various methods were examined in order to eliminate the defects
mentioned above, and it was discovered that a self-extinguishing
silicone rubber composition which can be cured to a silicone rubber
exhibiting an excellent self-extinguishing property and heat
stability, could be produced at a low cost without using platinum
or a platinum compound. A mixture of polydiorganosiloxane, aluminum
hydrate, and gamma-type iron sesquioxide or ferroferric oxide can
be cured to provide the stated properties.
DESCRIPTION OF THE INVENTION
This invention relates to a mixture comprising (A) 100 parts by
weight of a polydiorganosiloxane represented by an average unit
formula
wherein each R is selected from a monovalent hydrocarbon radical
and a halogen-substituted monovalent hydrocarbon radical, and a has
an average value of from 1.98 to 2.05, (B) 50 to 300 parts by
weight of aluminum hydrate with an average particle size of
.ltoreq.50 .mu.m, and (C) 0.1 to 30 parts by weight of an oxide
selected from the group consisting of gamma-type iron sesquioxide,
ferroferric oxide, and mixtures thereof, said oxide being in the
form of an extremely fine powder, and said ferroferric oxide having
a formula (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y in which the ratio
of x/y is from 0.05/1 to 1.0/1.
The polydiorganosiloxane used as component (A) is usually a
straight-chain polydiorganosiloxane with the general formula
R.sub.a SiO.sub.4-a /2 where each R represents a
halogen-substituted or unsubstituted monovalent hydrocarbon radical
selected from among methyl, vinyl, ethyl, propyl or aryl such as
phenyl, or their halogenated derivatives and a has an average value
of from 1.98 to 2.05. Examples of the units constituting the
polydiorganosiloxane are dimethylsiloxane, methylphenylsiloxane,
diphenylsiloxane, methylvinylsiloxane and phenylvinylsiloxane. The
form of the polydiorganosiloxane is arbitrary and ranges from
liquid to gum depending on the purpose. Homopolymers and
copolymers, and a mixture of homopolymer(s) and copolymer(s) can be
used. The degree of polymerization is 20 to 20,000. The preferred
polydiorganosiloxane is a gum-like polymer with a degree of
polymerization of .ltoreq.1000. A small quantity of RSiO.sub.1.5
can be contained in the above-mentioned structure. The ends of the
molecular chains are arbitrary and include hydroxyl, alkoxyl,
trimethylsiloxy, dimethylvinylsiloxy, methyldiphenylsiloxy and
methylphenylvinylsiloxy groups.
Aluminum hydrate used as component (B) is indispensable to the
self-extinguishing property of the silicone rubber mixture. The
average particle size of the aluminum hydrate should be .ltoreq.50
micrometers (.mu.m) in order to impart surface smoothness and the
self-extinguishing property to the cured silicone rubber. The
quantity of aluminum hydrate to be added is from 50 to 300 parts by
weight, preferably 100 to 200 parts by weight relative to 100 parts
by weight of (A). When the quantity of the aluminum hydrate in the
mixture is less than the value mentioned above, the silicone rubber
does not exhibit a satisfactory self-extinguishing property. On the
other hand, when the above-mentioned range of aluminum hydrate is
exceeded, the tensile strength and the volume resistivity of the
silicone rubber are impaired.
The general formulas of extremely fine powdery .gamma.-type iron
sesquioxide and fine powdery ferroferric oxide, component (C), are
respectively, .gamma.-Fe.sub.2 O.sub.3 and (FeO).sub.x (Fe.sub.2
O.sub.3).sub.y where the ratio of x/y is from 0.05/1 to 1.0/1.
Component (C) with component (B), is indispensable to the
self-extinguishing property of the silicone rubber. A common iron
oxide used in silicone rubber is .alpha.-Fe.sub.2 O.sub.3, which is
called "red oxide," however, a combination of .alpha.-Fe.sub.2
O.sub.3 and aluminum hydrate does not exhibit as strong a
self-extinguishing property as the combination of aluminum hydrate
and the 2 types of iron oxide of component (C) of this invention.
Gamma-type iron sesquioxide and ferroferric oxide can be used
together.
The particle size of .gamma.-type iron sesquioxide or ferroferric
oxide as a component of the mixture is extremely fine such as
.ltoreq.50 .mu.m. The quantity of this component to be added is 0.1
to 30 parts by weight, preferably 1 to 20 parts by weight relative
to 100 parts by weight of component (A). When the quantity of (C)
is less than 0.1 parts by weight, the resulting silicone rubber
does not exhibit a sufficient self-extinguishing property. On the
other hand, when the quantity of (C) exceeds 30 parts by weight,
the silicone rubber composition does not exhibit workability and
the elongation, tensile strength, volume resistivity and break down
voltage of vulcanized silicone elastomer are impaired.
A conventional curing agent, an organic peroxide, can be added to
and homogeneously mixed with the self-extinguishing silicone rubber
mixture of this invention before heat vulcanizing. Examples of
organic peroxide are benzoyl peroxide, 2,4-dichlorobenzoyl
peroxide, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, dicumyl
peroxide, monochlorobenzyl peroxide and t-butyl perbenzoate. The
preferred quantity of organic peroxide to be added is 0.3 to 6
parts by weight relative to 100 parts by weight of component
(A).
If necessary, in addition to the above-mentioned curing agent, an
organosilicon compound such as diphenylsilanediol, an alkoxysilane,
and low molecular weight hydroxyl endblocked polydimethylsiloxane
can be added to the self-extinguishing silicone rubber mixture.
Other self-extinguishing enhancing materials, such as finely
powdered copper, calcium carbonate, calcium zirconate, zirconium
silicate, manganese carbonate, titanium dioxide, cobalt organic
acid salts, organophosphorus compounds, azo and triazole compounds,
and essentially sulfur-free carbon black can be added. One or more
reinforcing fillers and bulking fillers can be also added. Examples
of the reinforcing fillers and bulking fillers are fumed silica,
precipitated silica, fine quartz powder, diatomaceous earth,
powdery zinc oxide, basic magnesium carbonate, active calcium
carbonate, magnesium silicate, aluminum silicate, talc, mica
powder, aluminum sulfate, calcium sulfate, barium sulfate,
asbestos, glass fiber, organic reinforcing agents and organic
fillers. In addition, traditional pigments, heat stability agents
such as cerium oxide and ceric hydroxide, and antioxidants can be
added.
The mixture is homogeneously kneaded using a roll or kneader mixer,
vulcanized at 100.degree.-450.degree. C. under elevated or ambient
pressure for several seconds to 1 hour, and then, if necessary,
secondarily heat-aged at 200.degree.-250.degree. C. for 1 to 48
hours in order to obtain the silicone rubber product having an
excellent self-extinguishing property.
This invention will be explained using demonstrative examples.
"Part" in the examples means "part by weight."
The self-extinguishing property was measured by the following
method. The heat-set silicone rubber was cut into test specimens,
130 mm-long, 13 mm-wide, 2 mm-thick. The test specimens were
clamped vertically in an area free from air currents. The bottom of
a test specimen was set on fire by nearly touching it with the
upper part of the inner flame of the flame of a Bunsen burner
(flame diameter, 11 mm; inner flame height, 20 mm and outer flame
height, 40 mm) for 15 seconds. The Bunsen burner was then removed
and the time (sec) required for the flame to die out was measured.
This flame test was conducted twice for each of 5 test specimens.
The average value (sec) was used as a measure of the
self-extinguishing property.
EXAMPLE 1
A base mixture of 100 parts of a dimethylvinylsiloxy endblocked
polydiorganosiloxane gum having a degree of polymerization of 5000;
99.5 mol% dimethylsiloxane units and 0.5 mol% methylvinylsiloxane
units, 4 parts hydroxyl endblocked polydimethylsiloxane having a
viscosity at 25.degree. C. of 0.00004 m.sup.2 /g, 120 parts of
aluminum hydrate having an average size of particle of 10 .mu.m and
45 parts of precipitated silica having a specific surface area of
230 m.sup.2 /g was homogeneously kneaded and then heated at
150.degree. C. for 2 hours. This base mixture in the amount of 100
parts was combined with 2 parts of .gamma.-Fe.sub.2 O.sub.3, 4
parts of FeO.Fe.sub.2 O.sub.3 and 0.5 part of
2,5-dimethyl-2,5-di(t-butylperoxy)hexane (curing agent) as shown in
Table 1. The resulting mixture was homogeneously kneaded using a
two-roll mixer in order to obtain the mixture to be molded.
The mixture was vulcanized at 170.degree. C. under an elevated
pressure of 2.94 megapascals (MPa) for 10 minutes. The
self-extinguishing property of the resulting 2 mm-thick silicone
rubber sheet was examined by the method mentioned above.
For comparative examples, silicone rubber sheets were produced by
the same method as described above with the exception that the
curing agent, 0.4 part of 2 weight percent H.sub.2 PtCl.sub.6
6H.sub.2 O in isopropyl alcohol (IPA) solution and the curing
agent, or 4 parts of .alpha.-Fe.sub.2 O.sub.3 and the curing agent
were added to the base mixture. The self-extinguishing property was
tested by the same method as described above. The results obtained
are given in Table 1.
The tensile strength and elongation were determined on the silicone
rubber of mixture 1 and comparative mixture 6 after vulcanization
and then after heat aging for 30 hours at 250.degree. C. The
results obtained are shown in Table 1.
TABLE 1
__________________________________________________________________________
This invention Comparative example 1 2 3 4 5 6 7
__________________________________________________________________________
Base mixture (parts) 100 100 100 100 100 100 100 .gamma.-Fe.sub.2
O.sub.3 (parts) 2 4 -- -- -- -- -- FeO . Fe.sub.2 O.sub.3 (parts)
-- -- 2 4 -- -- -- .alpha.-Fe.sub.2 O.sub.3 (parts) -- -- -- -- 4
-- -- H.sub.2 PtCl.sub.6 . 6H.sub.2 O (parts) -- -- -- -- -- 0.4 --
IPA solution Curing agent (parts) 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Self-extinguishing property First time (sec) 0 0 1 0 8 6 13 Second
time (sec) 10 12 8 5 25 24 60 Physical Properties Initial Tensile
Strength, MPa 5.20 -- -- -- -- 4.61 -- Elongation, % 225 -- -- --
-- 185 -- After heat aging at 250.degree. C./30 hours Tensile
Strength, MPa 3.92 -- -- -- -- 3.53 -- (% retention) (75.5) -- --
-- -- (76.6) -- Elongation, % 100 -- -- -- -- 50 -- (% retention)
(44.4) -- -- -- -- (27.0) --
__________________________________________________________________________
EXAMPLE 2
A mixture of 100 parts of dimethylvinylsiloxy endblocked
polydiorganosiloxane gum having a degree of polymerization of 7000;
99.8 mol % dimethylsiloxane units and 0.2 mol % methylvinylsiloxane
units, 4 parts of hydroxyl endblocked polydimethylsiloxanes having
a viscosity at 25.degree. C. of 0.00004 m.sup.2 /g, 180 parts of
aluminum hydrate having an average particle size of 10 .mu.m, and
30 parts of fumed silica having a specific surface area of 200
m.sup.2 /g was homogeneously kneaded and then heated at 150.degree.
C. for 2 hours in order to obtain the base mixture.
This base mixture in the amount of 100 parts was combined with 2
parts of .gamma.-Fe.sub.2 O.sub.3, 2 parts of FeO.Fe.sub.2 O.sub.3,
and 0.5 part of 2.5-dimethyl-2,5-di(t-butylperoxy)hexane (curing
agent). The resulting mixture was homogeneously kneaded using a
two-roll mixer in order to obtain the mixture to be molded. This
mixture was vulcanized at an elevated temperature by the same
method as in Example 1. The self-extinguishing property was tested
by the method mentioned above.
For comparative examples, silicone rubber sheets were produced by
the same method as mentioned above with the exception that the
curing agent, or either 5 parts of .gamma.-Fe.sub.2 O.sub.3 and
curing agent or 5 parts of FeO.Fe.sub.2 O.sub.3 and curing agent
were added to the base mixture to which aluminum hydrate had not
been added. The self-extinguishing property of these silicone
rubber sheets which had been vulcanized by the method mentioned
above were examined by the same method as described above.
The results obtained are given in Table 2.
TABLE 2 ______________________________________ This invention
Comparative example Base mixture 1 2 3 4 5
______________________________________ Gum (parts) 100 100 100 100
100 Hydroxyl endblocked polydimethylsiloxane (parts) 4 4 4 4 4
Aluminum hydrate 180 180 180 -- -- (parts) Fumed silica (parts) 30
30 30 30 30 Base mixture (parts) 100 100 100 100 100
.gamma.-Fe.sub.2 O.sub.3 (parts) 2 -- -- 5 -- FeO . Fe.sub.2
O.sub.3 (parts) -- 2 -- -- 5 Curing agent (parts) 0.5 0.5 0.5 0.5
0.5 Self-extinguishing property First time (sec) 0 0 10 * * Second
time (sec) 7 8 47 -- -- ______________________________________
*Total destruction by fire
* * * * *